A powerful data-snatching virus targeting computers in Iran, Israel and other Middle Eastern countries has been discovered by Russian experts. The worm has been used for years for what seems to be state-sponsored cyber espionage.

­Russian cyber-security company Kaspersky Lab says the malware, codenamed Flame, is the largest and one of the most complex cyber-attacks ever discovered. It reports that the most severely affected computers are in Iran – but Israel, Syria and other countries across the Middle East have also been infected.

Kaspersky's first recorded instance of Flame dates back to August 2010, although the firm admits the worm could have been stealing data for years before that.